Wet spinning process



March 26, 1957 s. G. HAWTIN ETAL 2,736,737

WET SPINNING PROCESS Filed March 27,":1951

Attorneys 2,786,737 WET SPINNING rnocuss Selwyn George Hawtin and JohnWilliam Grebby, Spondon, near Derby, England, assignors to BritishCelanese Limited, a corporation of Great Britain Application March 27,1951, Serial No. 217,816

Claims priority, application Great Britain March 28, 1950 6 Claims. (Cl.18-54) This invention relates to the manufacture of artificial fibres bywet spinning methods and to the treatment of fibres with liquids.

in one method of wet spinning multi-filament yarns, the spinningsolution is extruded through a spinning jet upwardly, for instancevertically upwards, into an upwardly flowing current of coagulatingliquid. For example a solution of cellulose acetate in acetone may beextruded into and set in an upwardly flowing current of aqueous acetone.The current of coagulating liquid may be contained in a substantiallyvertical tube of fairly narrow diameter (referred to below as a settingtube), preferably attached to a somewhat broader base containing the jetand the inlet for the coagulating liquid. The coagulating liquid mayoverflow at the top of the tube or may escape through orifices nearthetop of the tube, and may be led off forrecovery or re-use. Thefilaments leaving the setting tube are preferably carried upwardsthrough the atmosphere for a further distance and may then be led,preferably round one or more guides, through a further air-run to agodet feeding to a winding device. The filaments leaving the body ofcoagulating liquid in the setting tube normally carry with them a columnof coagulating liquid to a height depending inter alia on the number anddenier of the filaments and the "speed at which they are travelling, andthe abovementioned guide, or -the first guide if more than one isemployed, is advantageously positioned well above the top of this columnof coagulating liquid.

We have observed that when multi-filament yarns are made by the wetspinning method outlined above, the individual filaments remainseparate, from each other during the whole of their travel through thebody of the coagulating liquid, but come together at a point between thesurface of the liquid and the first guide, forming a narrow cone. Wehave also observed that, at least over a considerable range ofconditions, the height of the column of coagulating liquid carried upwith the filaments is approximately the same as the height of the-cone,in other words, when or soon after the filaments have come together theyno longer carry the column of coagulating liquid with them, though theyare of course still quite wet. The'point of convergence ofthe filaments,he the apex of the cone formed by the filaments as they come together,we call the node. The bundle of filamerits above the node is hereinafterreferred to as the yarn to distinguish it from the separatefilamentsbelow the node.

We have found that'by applying a false twist to the yarn by a devicesituated above the node, the position of the node may be lowered, forexample until it is at or below the surface of the coagulating liquid,and that when this is done the amount of coagulating liquid carried upby the filaments or yarn is reduced. If, as is preferred, the

2,786,737 Patented Mar. 26, 1957 node is forced right down to or belowthe surface of the liquid, the reduction in the amount of coagulatingliquid carried up is very considerable. This has a number'of advantages,for instance it facilitates winding, makes possible a shorter air-runfor the yarn, and reduces the amount of solvent which is lost, e. g. byevaporation, or which can be recovered only with considerable diflicultyand expense.

The application of a false twist in this way hasa similar effect inother processes in which a number of filaments passing through aliquidate brought together to form a yarn at a point (in the absence ofthe twist) above the surface of'the liquid.

According'to the invention, therefore, in a process in which a number offilaments pass separately in nearly parallel paths upwardly through aliquid and come together to form a yarn at a point which is above-thesurface of the liquid when the yarn is free from twist, the point atwhich the filaments come together is lowered by applying a false twistto the yarn. The invention also includes devices whereby the process canbe carried out and the false twist applied.

The invention is of particular importance in connection with verticalupward wet spinning processes'of the general type already indicated, andwill be described in more detail by reference to such a process and to aform of device'for carrying it out.

In a wet-spinning device constructed in accordance with the preferredform of the invention, the newly formed yarn passes first over a groovedpulley which is or can be fixedskew with respect to the natural plane ofthe yarn so as to cause the yarn when it first reaches the pulley tomake contact with one side of the groove, and at a later stage in itspassage over the pulley to make contact with the bottom of the groove.(By the natural plane of the yarn is meant the plane in which the yarnwould travel were the pulley replaced by a perfectly smooth rod havingits length substantially at right angles to the line of theyarnaproaching the pulley andthe line of the yarn leaving it.) Thegroove in the pulley must of course'be deep enough and narrow enough tocause the yarn to behave in the manner described when the pulley issuitablyfixed. lngeneral, the shallower and wider the groove the greaterwill -bethe angle at which the pulley must be set to produceagiveneffect. We prefer to use a pulley having an approximately V-s'hapedgroove whose greatest width is not more than about 3 times, andespecially not more than about twice, its depth. Preferably the pulley.is held in a mounting which can be turned about a horizontal axis, orat least about an axis having a considerable horizontal component, e. g.one set at 45 or less to the horizontal, to one side or to either sideout of the natural plane of the yarn, for example it maybe held in amounting which can be rotated'about-thc desired axis'and is providedwith means whereby itmay be fixed in the desired position. Alternativelythe pulley may for example be held in amounting which is pivoted aboutafvertica'l axis-lying in the natural plane of the yarn but outsidethepulley.

The 'amount'by which'the pulley is turned out ofthe natural plane ofthe-yarn determines the degree offalsc twist imparted to the yarn, andthus the degree by-which theno'de is fforced'down. 'Advantageously theyarn'in passing overthepulley changes its direction by about a rightangle; thus 'a substantially "vertical path may be changed toonesubstaritially' horizontal. The yarn may then begiven such fufther'din-run ,as may in 'any particular'instancebe necessary, andthen,ifdesireda'fterpassing 3 over one or more further pulleys or otherform of guide, it may be passed round a godet and wound up, or twistedand wound up, for instance as a cap-spun bobbin.

One embodiment of this invention is illustrated in the accompanyingdrawing, wherein:

l is a side view of a wet-spinning apparatus,

131g. 2 is a front View of a pulley used in this apparatus, an

Fig. 3 is a side view of this pulley.

The device shown in the drawing has been found to be very suitable forupwardly wet spinning yarns of cellulose acetate by extruding an acetonesolution of the cellulose acetate into a coagulating liquid consistingof an aqueous solution of acetone. The device comprises an extrusionchamber 1, a setting tube 2 of smaller diameter, suitable guides 3 and 4comprising free-running grooved pulleys, and a godet 5 feeding to awinding device (not shown). The extrusion chamber 1 is cylindrical inshape, and near its lower end is provided with inlets 6 for thecoagulating liquid, at a somewhat higher level a spinning jet 7 ismounted centrally in the chamber and facing upwards, and between thelevel of the inlets 6 for the coagulating liquid and the level of thejet face a horizontal perforated metal sheet 8 extends across the Wholeof the free space in the chamber to reduce turbulence in the coagulatingliquid. Above the jet face the cylindrical chamber 1 is joined, by aconverging section 9, to the setting tube 2, which is mounted verticallyabove the jet face. At its open upper end the setting tube 2 issurrounded by a funnel 10 fitted with a lead-off 11 for liquid, by meansof which the coagulating liquid as it overflows at the top of thesetting tube 2 is collected and led off for recovery or reuse.

The first guide pulley 3 is freely mounted vertically above the openupper end of the setting tube 2 in a mounting 12 attached to a rod 13which passes through and is held by a bearing block 14; the rod 13 canbe rotated in the bearing block 14, so causing the mounting 12 holdingthe pulley 3 to turn about a horizontal axis, and may be fixed in anydesired position by means of a set screw 15. The second guide pulley-4is freely mounted in a fixed mounting 15 at the same level as but aconsiderable distance from the first pulley 3; beneath this secondpulley 4 is the godet 5 and the winding up device, the whole arrangement being such that the yarn 17 passes over the two pulleys anddown to the godet, and in doing so runs through the atmosphere forseveral feet, say 5-15 feet, the best distance depending on variousfactors such as fyarn speed, yarn denier, and temperature.

By virtue of its swivel mounting the first of the free running pulleyscan be turned about a horizontal axis out 'of the plane in which theyarn would otherwise lie, so causing the yarn reaching the pulley tomake contact with one side of the groove. By adjusting the amount bywhich the pulley is so turned the node, i. e. the apex of the coneformed by the filaments as described above, can be forced down to or (asillustrated) below the level of the open end of the setting tube, soconsiderably reducing the amount of coagulating liquid carried up withthe filaments or yarn.

The device illustrated can be modified by providing a positive drive tothe first guide pulley 3. Although in most cases we prefer that thepulley should be free running, if only for the sake of simplicity, apositive drive may be used with advantage when spinning under conditionssuch that the tension in the yarn is very low. It is found that, for agiven skew position of the pulley, the position of the node can bevaried by changing the speed at which the pulley is driven.

While the invention has been described in connection with themanufacture of cellulose acetate yarns by a particular wet spinningprocess, it is applicable over a wider field. Thus it may be used in thewet spinning of multifilament yarns having a basis of a material otherthan cellulose acetate, whether it be another cellulose ester,

e. g. cellulose propionate; a cellulose ether, e. g. ethyl cellulose ora Water-soluble ether such as a methyl, hydroxy-ethyl, or sodiumcarboxy-methyl cellulose; or a non-cellulosic material, for example apolymerised vinyl halide, a co-polymer of a vinyl halide and a vinylfatty acid ester such as vinyl acetate, or polyacrylonitrile or aco-polymer of acrylonitriie with another vinyl compound. In the processparticularly described the coagula-ting liquid is an aqueous solution ofa volatile solvent for the cellulose acetate, namely acetone, but it mayin stead comprise a solvent of low volatility; thus in spinningcellulose acetate from acetone solution an aqueous solution ofdiethylene glycol diacetate may be used; in such a case no extendedair-run is needed, and residual diethylene glycol diacetate may besubsequently removed from the yarn by washing. Again, While in thewetspinning device particularly described the filaments are set in aco-current of coagulating agent, a counter-current or transverse currentmay be used, or the filaments may be set in a large volume ofcoagulating agent which is changed at a suitable rate but which does notflow as a whole at any considerable speed in any direction. Either asingle jet or a number of jets may be used in the one coagulating bath.

The invention may also be applied to processes other than wet-spinning,in which a number of separate filaments pass through a liquid and arethen wound up as a single yarn; the filaments may be single continuousfilaments, or may each be made up of a number of single continuousfilaments or of staple fibre. Such processes may have as their objecteither to alter the properties of the material in some way, e. g. to dyeit or to shrink it, or to apply a removable coating or other substanceto the surface of the filaments, e. g. a size or anti-static dressing or(in the case of thermoplastic materials) a softening agent orplasticiser. The degree of false twist applied may be such as to reduceto a minimum the amount of liquid adhering to the yarn, or to adjust itto some desired value above the minimum. The application of theinvention is not restricted to processes in which, in the absence of thefalse twist, the filaments or yarn carry with them a column of thecoagulating or treating liquid.

If desired, instead of the false twist a true twist to a similar degreemay be inserted in the yarn, but this will usually be much lessconvenient.

Having described our invention, what we desire to secure by LettersPatent is:

1. A process for the production of yarn by the wet spinning method,which comprises extruding a spinning solution into a setting liquid toform a number of filaments, drawing the filaments by a yarn forwardingmeans upwardly in nearly parallel paths through and once for all out ofthe liquid under conditons such that they come together to form a yarnat a point which would be between the surface of the liquid and the yarnforwarding means were the yarn free from twist, and changing thedirection of travel of the yarn by passing it over a grooved pulleyfixed skew with respect to the natural plane of the yarn, the saidpulley being the first structure with which the yarn makes contact afterthe filaments have left the setting liquid, and the shape of the grooveand the position of the pulley being such that the yarn when ittreachesthe pulley makes contact with one side only of the groove and at a laterstage in its passage over the pulley makes contact with the bottom ofthe groove, whereby a false twist is applied to the yarn and the pointat which the filaments come together is lowered.

2. Process according to claim 1, wherein the groove in the pulley is ofapproximatey V-shaped section having its greatest width at the mostthree times its depth, and the plane of the pulley is rotated out of thenatural plane of the yarn about an axis at an angle of 0 to 45 to thehorizontal. g 7 Q I 3. Process according to claim 2, wherein the pulleyis free running. I i

References Cited in the file of this patent UNITED STATES PATENTSSchrenk Aug. 7, 1934 Dickie et al Dec. 31, 1935 Oppenlaender Feb. 8,1938 Polak May 9, 1944 Whisnant Jan. 30, 1951

1. A PROCESS FOR THE PRODUCTION OF YARN BY THE WET SPINNING METHOD,WHICH COMPRISES EXTRUDING A SPINNING SOLUTION INTO A SETTING LIQUID TOFORM A NUMBER OF FILAMENTS, DRAWING THE FILAMENTS BY A YARN FORWARDINGMEANS UPWARDLY IN NEARLY PARALLEL PATHS THROUGH ONE ONCE FOR ALL OUT OFTHE LIQUID UNDER CONDITIONS SUCH THAT THEY COME TOGETHER TO FORM A YARNAT A POINT WHICH WOULD BE BETWEEN THE SURFACE OF THE LIQUID AND THE YARNFORWARDING MEANS WERE THE YARN FREE FROM TWIST, AND CHANGING THEDIRECTION OF TRAVEL OF THE YARN BY PASSING IT OVER A GROOVED PULLEYFIXED SKEW WITH RESPECT TO THE NATURAL PLANE OF THE YARN, THE SAIDPULLEY BEING THE FIRST STRUCTURE WITH WHICH THE YARN MAKES CONTACT AFTERTHE FILAMENTS HAVE LEFT THE SETTING LIQUID, AND THE SHAPE OF THE GROOVEAND THE POSITION OF THE PULLEY BEING SUCH THAT THE YARN WHEN IT REACHESTHE PULLEY MAKES CONTACT WITH ONE SIDE ONLY OF THE GROOVE AND AT A LATERSTAGE IN ITS PASSAGE OVER THE PULLEY MAKES CONTACT WITH THE BOTTOM OFTHE GROOVE, WHEREBY A FALSE TWIST IS APPLIED TO THE YARN AND THE POINTAT WHICH THE FILAMENTS COME TOGETHER IS LOWERED.